Foams are widely used to remove liquid loading at the bottom of gas wells to improve natural gas production. However, it becomes ineffective when a gas well contains a large amount of hydrocarbon condensate because oil will rupture the foams. In this work, condensate oil-tolerant foams were developed and stabilized by a mixture of cocamidopropyl hydroxyl sulfobetaine (CHSB) and sodium dodecyl sulfate (SDS). The foam properties are examined at different temperatures under atmospheric conditions and high pressures with various contents of condensate oil. It is found that the foam stability is improved when the oil content is increased; in addition, high temperature, high salinity, and high pressure are beneficial for foam stabilizing. To reveal the mechanism of stable foam in the presence of high content of oil, a confocal microscope was employed to visualize oil–foam interactions. It was observed that the high stability of the SDS–CHSB foams is ascribed to the formation of stable pseudoemulsion between oil droplets and the gas–liquid interface. Such condensate oil-tolerant foams show promising potential to be used in the foam-assisted lift process during natural gas production.

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Deliquification with chemical foamers has proved a successful and economic technique to unload the liquids from mature natural gas wells; however, no gases are available to create foams in the low-productivity gas wells. In this work, in situ generated foams (ISGF) were developed with the gas and heat produced by the reaction of ammonium chloride and sodium nitrite in the presence of acetic acid as a catalyst, with the mixture of sodium dodecyl sulfate and cocamidopropyl hydroxyl sulfobetaine as the foamer. The molar ratio of reactants to catalyst, and the specifies of ammonium salt were optimized based on the foamability and stability of the foams. The volume of gas and the amount of heat were measured from the optimized gas-and heat-generated system. The morphology of the ISGF foams was found to be more uniform than their conventional counterpart, and these foams exhibited superior foaming at high temperature and high salinity. The optimized formulation was scaled up and applied in two typical lowproductivity gas wells, and significant increment in gas production and decline in water production were found. The ISGF foams not only offer a choice to unload liquids from mature gas wells by providing gas to create foams and to offer heat to dissolve organic pollutants but also provide candidature techniques for unconventional gas wells to prolong life spans.

ObjectiveTo investigate the use of video display terminal (VDT) in high-altitude regions by medical students and the resulted risk factors of eye discomfort.MethodsA cross-sectional study was conducted in 686 medical students randomly selected from high-altitude regions, Kunming, Yunnan Province. The prevalence of video display terminal syndrome (VDTs) and related risk factors in medical students were analyzed by instructing students to fill in the eye discomfort symptom questionnaire [Ocular Surface Disease Index (OSDI) scale].ResultsThere were 686 participants in this study, including 213 males (31.0%) and 473 females (69.0%). The results of questionnaire survey showed that 184 patients (26.8%) didn't have eye discomfort symptoms and 502 patients (73.2%) had eye discomfort symptoms. The comparison of demographic and ocular characteristics of eye discomfort symptoms group and no eye discomfort symptoms group showed that medical students in the group with ocular discomfort symptoms had longer total duration of video terminal use, longer duration of each VDT use, higher total scores of ocular discomfort symptom scores, and a higher percentage of the ocular discomfort severity group, all with statistically significant differences. There was no significant difference in the remaining parameters between the two groups of participants. The results of multivariate logistic regression model analysis showed that the relationship between total sleep time, total duration of VDT use and eye discomfort symptom score was statistically significant (P < 0.05). Besides, ordinal logistic regression was applied further to investigate related factors of the severity of eye discomfort. The model demonstrated that total sleep duration and total VDT using duration were significantly associated with the severity of eye discomfort symptom (P < 0.05).The severity of eye discomfort symptom was significantly negatively related to the increased total sleep duration and it was significantly positively related to the increased VDT use duration.ConclusionThe prevalence of VDTs is high in medical students at high-altitude regions. The longer total duration of daily use of VDT and shorter sleep duration are risk factors associated with VDTs. The severity of eye discomfort symptom was significantly negatively related to the increased total sleep duration and it was significantly positively related to the increased total VDT using duration.